Antimicrobial solid surface materials containing chitosan-metal complexes

ABSTRACT

A solid surface material with an antimicrobial agent in a thermoset and/or thermoplastic resin matrix where the antimicrobial agent comprises a chitosan-metal complex.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.10/324,803 filed Dec. 20, 2002 now abandoned, which claims the benefitof Provisional Application No. 60/343,321 filed Dec. 21, 2001, both ofwhich are hereby incorporated by reference.

FIELD OF INVENTION

This invention is directed to solid surface materials havingantimicrobial properties.

BACKGROUND OF THE INVENTION

Artificial or synthetic marble is a general designation for varioustypes of materials used as building products, such as bathroom vanitytops, sinks, shower stalls and kitchen counter tops, and otherdecorative surfaces. It is also a suitable material for use infurniture, lining materials, and in stationary small articles. Theartificial marble is easily kept clean and neat. Therefore, it hasincreasingly been used in hospitals, nursing homes, as well as incommercial and residential food preparation facilities.

Artificial marbles encompass cultured marble, onyx and solid surfacematerials typically comprising some kind of resin matrix and either withor without a filler present in the resin matrix. Typically, culturedmarble is made of a gel coating of unfilled unsaturated polyester on asubstrate of a filled unsaturated polyester. The filler may be calciumcarbonate or a similar material. Onyx typically consists of a gel coatof unfilled unsaturated polyester on a substrate of filled unsaturatedpolyester. The filler in this case is typically alumina trihydrate(ATH). Solid surface materials are typically filled resin materials and,unlike cultured marble or onyx, do not have a gel coat. Corian® materialavailable from E. I. du Pont de Nemours and Company (DuPont),Wilmington, Del., is a solid surface material comprising an acrylicmatrix filled with ATH. Another solid surface DuPont material, known bythe brand name Zodiaq®, is alternatively described as an engineeredstone or artificial granite. Such materials are made from an unsaturatedpolyester matrix filled with quartz or other similar fillers.

As evidenced by numerous materials in the market, there is clearly ademand for materials and/or processes that either minimize or killharmful microorganisms encountered in the environment. Such materialsare useful in areas for food preparation, processing, service orhandling. Such materials will also be useful in areas for personalhygiene, such as bathroom facilities. Similarly, there is a use for suchantimicrobial materials in hospitals and nursing homes where people withlowered resistance are especially vulnerable to pathogenicmicroorganisms.

Solid surface materials made of either an acrylic resin, an unsaturatedpolyester resin, an epoxy resin, or other such resins and incorporatingcertain antimicrobial agents throughout the resin are described in WO97/49761 (E. I. du Pont de Nemours and Company). However, suchantimicrobial agents can be expensive, resulting in a high installationcost for the resulting solid surface material.

Chitosan and chitosan-metal compounds are known to provide antimicrobialactivity as bacteriocides and fungicides (see, e.g., T. L. Vigo,“Antimicrobial Polymers and Fibers: Retrospective and Prospective,” inBioactive Fibers and Polymers, J. V. Edwards and T. L. Vigo, eds., ACSSymposium Series 792, pp. 175-200, American Chemical Society, 2001).Chitosan is also known to impart antiviral activity, though themechanism is not yet well understood (see, e.g., Chirkov, S. N., AppliedBiochemistry and Microbiology (Translation of Prikladnaya Biokhimiya iMikrobiologiya) (2002), 38(1), 1-8).

Chitosan is the commonly used name for poly-[1-4]-β-D-glucosamine.Chitosan is chemically derived from chitin (apoly-[1-4]-β-N-acetyl-D-glucosamine) which, in turn, is derived from thecell walls of fungi, the shells of insects, and, especially,crustaceans. Thus, it is inexpensively derived from widely availablematerials. It is available as an article of commerce from, for example,Primex (Iceland); Biopolymer Engineering, Inc. (St. Paul, Minn.);Biopolymer Technologies, Inc. (Westborough, Mass.); and CarboMer, Inc.(Westborough, Mass.). Chitosan can also be treated with metal-saltsolutions so that the metal ion forms a complex with the chitosan. Forexample, U.S. Pat. Nos. 5,541,233 and 5,643,971 disclose a process forpreparing durable antimicrobial agents by treating a chitosan suspensionwith metal salts of zinc and copper followed by chelation of apotentiator such as an imidazole. Application WO 99/37584 discloses thepreparation of chitosan-zinc sulfate, copper sulfate and silver nitratecomplexes for treating water to reduce levels of pathogens.

In commonly assigned U.S. patent application Ser. No. 60/290,297 (filed11 May 2001), chitosan (in the form of an acidic solution applied topolyester articles) is shown to impart antimicrobial activity. Thechitosan-treated article may be treated subsequently with a solution ofzinc sulfate, cupric sulfate, or silver nitrate to enhance antimicrobialactivity.

Cultured marbles have been developed incorporating an antimicrobialagent in the gel coat only (i.e., not throughout the matrix of thesubstrate). Such materials have been disclosed in Japanese PatentApplication Publication Kokai: 7-266522. These materials have arelatively thin gel coat, typically on the order of 15 mils. As such,when the gel coat is depleted of antimicrobial agent or the gel coatwears away or is otherwise removed, the antimicrobial effect of the gelcoat is significantly decreased or lost entirely.

The problem that remains to be solved is to provide solid surfacematerials comprising either an acrylic resin, an unsaturated polyesterresin, an epoxy or other similar resin and an effective antimicrobialagent dispersed throughout the resin.

SUMMARY OF THE INVENTION

This invention is directed to a solid surface material comprising amatrix of at least one resin, and an antimicrobial agent dispersed inthe matrix. The antimicrobial agent is a chitosan-metal complex, whichis prepared under homogeneous conditions and isolated as a product. Theresin can be thermoset, thermoplastic, or combinations thereof.Optionally, at least one filler can be dispersed in the matrix.

In a preferred embodiment, the resin is made from a syrup comprising anacrylic group polymer dissolved in a material selected from the group ofan acrylic group monomer solution and a mixed monomer solutioncontaining a vinyl monomer for copolymerization with an acrylic groupmonomer as a main component; the filler is alumina trihydrate; and theantimicrobial agent comprises a complex of chitosan with silver or asilver compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results of Corian® material with 0.5%, 1.0%, and 3.0%chitosan content vs. Escherichia coli (ATCC 25922).

FIG. 2 shows the results of Corian® material with 0.1%, 0.25%, 0.5%, and1.0% chitosan-silver nitrate content vs. Escherichia coli (ATCC 25922).

FIG. 3 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190% and 0.380% silver nitrate content vs.Escherichia coli (ATCC 25922). The respective chitosan to silver ratiosas determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05, 1:0.095, and1:0.105.

FIG. 4 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Listeria weshimeri (ATCC 35897). The respective chitosan to silverratios as determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05,1:0.095, and 1:0.105.

FIG. 5 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Candida albicans (ATCC 10231). The respective chitosan to silver ratiosas determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05, 1:0.095, and1:0.105.

FIG. 6 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Staphylococcus aureus (ATCC 6538). The respective chitosan to silverratios as determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05,1:0.095, and 1:0.105.

FIG. 7 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Escherichia coli (O157:H7). The respective chitosan to silver ratios asdetermined by ICP analysis are 1:0.016, 1:0.022, 1:0.05, 1:0.095, and1:0.105.

FIG. 8 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Klebsiella pneumoniae (ATCC 4352). The respective chitosan to silverratios as determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05,1:0.095, and 1:0.105.

FIG. 9 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Salmonella cholerasuis (ATCC 9239). The respective chitosan to silverratios as determined by ICP analysis are 1:0.016, 1:0.022, 1:0.05,1:0.095, and 1:0.105.

FIG. 10 shows the results of Corian® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Escherichia coli (O157:H7) in the presence of BSA. The respectivechitosan to silver ratios as determined by ICP analysis are 1:0.016,1:0.022, 1:0.05, 1:0.095, and 1:0.105. Corian® AB™ material is anantimicrobial Corian® material containing silver zirconium phosphate andis used in this experiment as a putative positive control. The silverzirconium phosphate active was rendered inactive against this bacteriumin the presence of BSA.

FIG. 11 shows the results of Corian(® material with 1% chitosan and0.0237%, 0.0475%, 0.095%, 0.190%, and 0.380% silver nitrate content vs.Escherichia coli (ATCC 25922) in the presence of BSA. The respectivechitosan to silver ratios as determined by ICP analysis are 1:0.016,1:0.022, 1:0.05, 1:0.095, and 1:0.105.

FIG. 12 shows the results of Corian® material with chitosan-zinc sulfatevs. Escherichia coli (ATCC 25922).

FIG. 13 shows the results of Corian® material with chitosan-zinc sulfatevs. Staphylococcus aureus (ATCC 6538).

FIG. 14 shows the results of Corian® material with chitosan-zinc sulfatevs. Candida albicans (ATCC 10231).

FIG. 15 shows the results of Corian® material with chitosan-coppersulfate vs. Escherichia coli (ATCC 25922).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The artificial marbles of the present invention are made from a curableresin composition containing a chitosan-metal complex as anantimicrobial agent. As used herein, by the term “complex” is meant acompound in which the bonding occurs by interaction of the electrons ofthe donor with the empty orbitals of the acceptor. In some complexes,the electron flow may take place in both directions simultaneously. (ANew Dictionary of Chemistry, Fourth Edition, L. M. Miall and D. W. A.Sharo (eds.), John Wiley & Sons, Inc., New York, N.Y. (1968), p. 157).The preferred embodiment of the invention comprises a chitosan-silvercomplex.

The artificial marble materials of this invention are effective ininhibiting or destroying many common harmful microorganisms encounteredin the home, health care, and food preparation environments.Microorganisms commonly found in such environments, particularly whensuch environments remain wet, moist, or damp, include bacteria, yeasts,fungi, and viruses. Examples include, but are not limited to,Escherichia coli, Candida albicans, Staphylococcus aureus, Salmonellacholerasuis, Listeria weshimeri, and Klebsiella pneumoniae.

The present invention is directed to antimicrobial solid surfaces. By“antimicrobial” herein is meant bacteriocidal, fungicidal, andantiviral. The term “microbe” will similarly be used to mean abacterium, fungus, or virus. The term “antimicrobial effectiveness” isintended to mean that, given a sufficient amount of antimicrobial agent,the microbial concentration of a sample is decreased by at least a 3-logfactor (i.e., 99.9%) over a period of time. The actual antimicrobialeffectiveness of an antimicrobial agent depends upon the specific resinmatrix used and the specific bacteria tested.

The term “solid surface materials” herein refers to materials that areessentially non-porous composites of finely divided mineral fillersdispersed in an organic polymer matrix. As used herein, the term“organic polymer matrix” is synonymous with “resin matrix”. Solidsurface materials include, for example, materials useful for decorativesolid surfaces such as, for example, those used as building productssuch as bathroom vanity tops, sinks, shower stalls and kitchencountertops. Furniture, sanitary use, lining materials, and variousarticles such as office supplies and store fixtures may also beconstructed of solid surface materials.

Resin Matrix Materials

Solid surface materials comprise a resin matrix. The term “matrix” asused herein refers to the polymeric resin component in which fillers andother additives may be dispersed. The types of resin matrices useful inthe present invention include thermoplastic resins, thermoset resins,and combinations thereof. Thermoplastic resins include olefins (such aslow and high-density polyethylene and polypropylene), dienes (such aspolybutadiene and Neoprene® elastomer), vinyl polymers (such aspolystyrene, acrylics, and polyvinyl chloride), fluoropolymers (such aspolytetrafluoroethylene), and heterochain polymers (such as polyamides,polyesters, polyurethanes, polyethers, polyacetals and polycarbonates).Thermoset resins include phenolic resins, amino resins, unsaturatedpolyester resins, epoxy resins, polyurethanes, and silicone polymers.

Epoxy resins useful in the present invention include epoxy resins ofbisphenol type A, bisphenol type F, phenol novolak type, alicyclicepoxy, halogenated epoxy, and cycloaliphatic epoxy resins.

Unsaturated polyester resins useful in the present invention includethose wherein the reactivity is based on the presence of double ortriple bonds in the carbon atoms. Unsaturated polyester resins areformed by the reaction of molar amounts of unsaturated and saturateddibasic acids or anhydrides with glycols. The unsaturation sites canthen be used to cross-link the polyester chains, via vinyl-containingmonomers such as but not limited to styrene, MMA, or combinations ofstyrene/MMA into a thermoset plastic state.

As is known to those of ordinary skill in the art, there can be manyadditives to epoxy or unsaturated polyesters. Typically, such materialsare cured by adding cross-linking agents and catalysts to enhance thecross-linking action.

Acrylic resins useful in the present invention are not limited as longas the resin can be formed into an acrylic solid surface material bycuring. Examples of useful acrylic resins include various kinds ofconventional acrylic group monomers, acrylic group partial polymers,vinyl monomers for copolymerization other than acrylic group monomers,or partial polymers. As the acrylic group monomer, (meth)acrylic esteris preferable. As used herein, “(meth)acrylic” is understood to mean“acrylic and/or methacrylic”. Examples of (meth)acrylic esters includemethyl (meth)acrylic ester, ethyl (meth)acrylic ester, butyl(meth)acrylic ester, 2-ethylhexyl (meth)acrylic ester, benzyl(meth)acrylic ester, glycidyl (meth)acrylic ester.

An example of a useful solid surface material including acrylic resin isthe Corian® material, which includes a poly(methyl methacrylate) (PMMA)resin with ATH as a filler. Another example of a useful solid surfacematerial is Zodiaq® material, which comprises an unsaturated polyester(UPE) resin with a quartz or other silica filler. Both Corian® materialand Zodiaq® material can contain pigments, reground self material inparticulate form, and other additives as disclosed in U.S. Pat. Nos.3,847,865 and 4,085,246, both incorporated by reference herein.

Antimicrobial Agent

The solid surface materials of the present invention comprise at leastone antimicrobial agent that is dispersed in the resin matrix of thesolid surface material in an amount that provides the solid surfacematerial with an antimicrobial effectiveness as measured at an outersurface. The term “dispersed” herein means that the antimicrobial agentof the invention is present throughout the bulk of the solid surfacematerial of the invention and not just on the surface of the solidsurface material. The antimicrobial agent is provided in an amount thatresults in antimicrobial effectiveness, i.e., a 3-log reduction in thenumber of microorganisms, within about 24 hours from application asmeasured by the “Antimicrobial Hard Surface Test” and “AntimicrobialHard Surface Wipe Test” methods described below.

The amount of antimicrobial agent is preferably at least about 0.5 to 8%by weight of the precured total composition and, more preferably, atleast about 1% by weight of the precured total composition. It ispreferred that the antimicrobial agent be added and dispersed into theresin component. Chitosan-silver complex, for example, may be added tothe MMA before polymerization. Chitosan-silver complex may be added tothe UPE before mixing with quartz or other silica and thenvibrocompacted. Further processing (polymerization) does not alter theantimicrobial features of the agent.

The antimicrobial agent comprises a complex of chitosan and a metal,preferably silver, copper, or zinc. The metal or metal compounds can bepresent in amounts of 1% to 14% by weight based on the chitosan. Thesematerials were ground to about 400 mesh size for use as additives in thepreparation of polymers. While 400 mesh size was used for theembodiments of the Examples, the range of the particle size may be fromabout 100 mesh and smaller. Chitosan-silver complex is preferred for itssuperior antimicrobial efficacy.

The chitosan-silver complex used in the present invention is prepared byslowly adding a solution of silver salt to a chitosan solution such thata clear, colorless gel results. Typically, the silver salt solution is0.5 to 20 wt % silver nitrate in water. The chitosan solution comprises0.25% to 8.0% by weight chitosan in a dilute (0.25 to 5.0% by volume)aqueous solution of acetic acid. Typically, the chitosan is a 0.75% or1.5% by volume aqueous acetic acid solution containing 2% by weightchitosan.

When acidic aqueous solution is added to the chitosan-silver gel, asolution results that can be used, for example, as a finish. A solidform of the complex can be produced from the gel by a method comprisingthe following steps:

-   -   (i) adding water to the gel, with stirring;    -   (ii) raising the pH to the product of step (i) to pH 7 to 8 by        adding a basic solution as is commonly known in the art;    -   (iii) filtering the product of step (ii);    -   (iv) washing the filtered solids with water, then with        acetonitrile;    -   (v) drying the washed solids under vacuum; and    -   (vi) optionally, grinding the dried product to a fine powder.        Typically, deionized water is used throughout and the pH is        raised in step (ii) by dropwise addition of aqueous ammonium        hydroxide or substituted ammonium hydroxide. The complex can        then be added as a powder of desired particle size for the        preparation of materials described herein.

As opposed to a heterogenous synthesis of chitosan-silver complex inwhich chitosan as an insoluble aqueous suspension is treated with asolution of silver nitrate (see, for example, “Characterization ofSilver-binding Chitosan by Thermal Analysis and Electron Impact MassSpectrometry,” C. Peniche-Covas, M. S. Jimenez, A. Nunez, CarbohydratePolymers (1988), 9, 249-256), the homogenous synthesis demonstrated hereaffords fibrous material with excellent swelling properties suitable forhydrogel applications, for example, as the absorbent element in adiaper, incontinence pad or garment, panty liner, tampon, or sanitarynapkin.

In addition, the chitosan-silver complex powder can be reconstituted inaqueous solution and applied to a wide variety of surfaces, such as, butnot limited to, polymers and ceramics. For example, chitosan-silverpowder can be dissolved in 1-4% aqueous acetic acid solution to prepare1-4% chitosan-silver solution that can be applied as a finish or thepowder can be dissolved readily in 1-4% chitosan solution to give silverof desired concentration. The preferred surface comprises at least onenaturally occurring or synthetic polymer, such as, but not limited to,those polymers described in commonly assigned U.S. patent applicationSer. Nos. 10/288,762 and 10/919,844, U.S. Patent Application PublicationNo. 2003/0017194, and U.S. patent application Ser. No. 60/619,755 (filedOct. 18, 2004, titled “Process for Making Antimicrobial PolymerArticles”), all of which are hereby incorporated by reference.

Examples of suitable naturally occurring polymers include but are notlimited to cotton, wood, flax, shellac, silk, wool, natural rubber,leather, and mixtures thereof. Examples of suitable synthetic polymersinclude but are not limited to homopolymers, copolymers, mixtures, andblends of polyesters, polyetheresters, polyethers, polyamides,polyimides, polyetherimides, polyacetals, polystyrene, polyphenyleneoxide, polyphenylene sulfide, polysulfones, poly(meth)acrylates, liquidcrystalline polymers, polyetherketones, fluorine-containing polymers,acrylonitrile-styrene-butadiene resins, styrene-butadiene blockcopolymers, polycarbonates, cellulose-based polymers (e.g., cellulose,rayon, cellulose acetate), urea formaldehyde resins, polyacrylonitrile,epoxy resins, polyurethanes, melamine-formaldehyde resins, silicones,butyl rubber, polychloroprene, and polyolefins.

Blends of naturally occurring polymers and synthetic polymers are alsocontemplated. For example, wood pulp (WP)/polyester (PET) blends cancontain 1-100% WP and 100-1% PET. Typical WP/PET blends include, forexample, 55% pine WP/45% PET (2 oz/yd²), 55% cedar WP/45% PET (1.5oz/yd²), 70% rayon/30% PET intimate fiber blend (8 mesh pattern, 2.2oz/yd²), 50% lyocell/50% PET intimate fiber blend (1.8 oz/yd²), or 55%cedar WP/45% PET (2 oz/yd²).

Examples of suitable polyolefins for use in the present invention arepolypropylene, e.g., atactic polypropylene, isotactic polypropylene,syndiotactic polypropylene, biaxially oriented polypropylene (BOPP),metallocene-catalyzed polypropylene; polyethylene, e.g., high densitypolyethylene (HDPE), low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), metallocene-catalyzed polyethylene, very lowdensity polyethylene (VLDPE), ultrahigh molecular weight polyethylene(UHMWPE), high performance polyethylene (HPPE); copolymers of ethyleneand propylene; copolymers derived from ethylene or propylene and atleast one monomer chosen from propylene, methyl acrylate, ethylacrylate, n-butyl acrylate, methyl methacrylate, acrylic acid,methacrylic acid and carbon monoxide; and copolymers of olefins with adiolefin, such as a copolymer of ethylene, or of propylene, or ofethylene and other olefins, with: linear aliphatic nonconjugated dienesof at least six carbon atoms (such as 1,4-hexadiene) and other dienes,conjugated or not, such as norbornadiene, dicyclopentadiene, ethylidenenorbornene, butadiene, and the like. Other suitable polymers arecopolymers of ethylene and tetrafluoroethylene, such as Tefzel® ETFEfluoropolymer resin available from E. I. du Pont de Nemours & Co., Inc.(Wilmington, Del.).

Other polymers suitable for coating with the chitosan-silver complexsolution are ionomers. The term “ionomer” as used herein refers to apolymer with inorganic salt groups attached to the polymer chain(Encyclopedia of Polymer Science and Technology, 2nd ed., H. F. Mark andJ. I. Kroschwitz eds., vol. 8, pp. 393-396). Some examples of ionomersthat have been commercialized are Surlyn® thermoplastic resin availablefrom E. I. du Pont de Nemours & Co., Inc. (Wilmington, Del.) and Nafion®perfluorinated sulfonic acid membranes, also from DuPont. Polyesters andpolyamides that have been polymerized with a low level of sulfonatedcomonomer to enhance textile dyeability (see, e.g., U.S. Pat. Nos.5,559,205; 5,607,765; and 3,389,549) and sulfonated aromatic polyamides(see, e.g., U.S. Pat. Nos. 3,567,632 and 4,595,708) such as those usedin reverse osmosis membranes and other selective separation membranesare also suitable substrates to be coated with the chitosan-silvercomplex solution.

The chitosan-silver powder retains its integrity over long storageperiods, for example, more than a year of shell life without becomingextremely colored.

Fillers and Other Additives

Fillers useful in the present invention include, for example, aluminatrihydrate (ATH), alumina monohydrate (AMH), Bayer hydrate (BayH),quartz and other forms of silica (SiO₂), magnesium hydroxide (Mg(OH)₂),calcium carbonate (CaCO₃), barium sulfate (BaSO₄) or decorative agents(e.g., mica, glass chips, clear acrylic chips, “color flop” pigments(pigments that change color as the angle of viewing changes)), as a listthat is not exhaustive and not intended to limit the invention. Fillerscan be present in amounts up to about 95% by weight. Typically, but notnecessarily, the amount of filler is decreased by the weight percent ofantimicrobial agent added.

Solid surface materials may also include functional or decorativeadditives such as pigments, dyes, flame retardant agents, partingagents, fluidizing agents, viscosity control agents, curing agents,antioxidants, and the like as may be known to those of ordinary skill inthe art.

Uses

Solid Surface Materials

Solid surface materials of this invention are typically formed bycasting into a sheet form or casting into a shape form such as a sink,for example. Solid surface materials of this invention can also beproduced by, for example, compression molding, injection molding,extrusion, or vibrocompaction methods.

It is especially preferred that the solid surfaces of the presentinvention remain wet, damp or moist for optimum effectiveness. Examplesof solid surfaces of the present invention include, but are not limitedto, surfaces in home bathrooms, public restrooms, swimming pool areas,dormitories, stadiums, and athletic facilities: sinks, counter tops,shower walls and bases, and other walls that become wet during use. Inmedical care facilities, such as hospitals, clinics, medical vans, andnursing homes, the current invention provides antimicrobial protectionin the form of surfaces for counter tops, sinks, shower walls and bases,and back splashes in, for example, patient rooms, laundry rooms, soiledlinen areas, staff and visitor areas, intensive care and coronary careunits.

The present invention is also useful for antimicrobial protection wherethere is indirect food contact with the solid surface. Some examplesare: counter tops, sinks, back splashes, and table tops in kitchens;table tops, salad bar counters and shields, food lag areas, dirty dishareas, and dish washing and drying areas in restaurants and fast foodestablishments; certain areas in slaughterhouses where the nutrientinsult is not excessive; table, counter top, and back splash areas incanning, freezing, red meat packing, and bread and pastry productionfacilities; and grocery and fresh food counter tops, displays, and otherfixtures in a grocery store.

The present invention is also useful for the surfaces of writinginstruments, such as pens and pencils, since pathogenic microorganismsare easily transmitted by hand contact, and perspiration would increasethe antimicrobial efficacy.

Chitosan-Silver Complex

The chitosan-silver complex, which is dispersed in the solid surfacematerials of the present invention, can be used by itself to impartantimicrobial and antiodor functionality in a wide variety ofapplications. For example, a reconstituted solution of thechitosan-silver complex can be used as a finish solution for textilesapplications as is commonly performed in the art.

Typically, a solution of the complex would be applied to an article'ssurface by any convenient means, such as but not limited to dipping,padding, or spraying, in a batch or continuous mode.

Articles comprising polymeric material treated with the chitosan-silvercomplex may be in the form of or comprise a film, membrane, laminate,knit fabric, woven fabric, nonwoven fabric, fiber, filament, yarn,pellet, coating, or foam. Articles may be prepared by any means known inthe art, such as, but not limited to, methods of injection molding,extruding, blow molding, thermoforming, solution casting, film blowing,knitting, weaving, or spinning.

Such articles include packaging for food, personal care (health andhygiene) items, and cosmetics. By “packaging” is meant either an entirepackage or a component of a package. Examples of packaging componentsinclude, but are not limited, to packaging film, liners, absorbent padspackaging, shrink bags, shrink wrap, trays, tray/container assemblies,caps, adhesives, lids, and applicators. Such absorbent pads, shrinkbags, shrink wrap, and trays of the present invention are particularlyuseful for packaging meat, poultry, and fish.

The package may be in any form appropriate for the particularapplication, such as a can, box, bottle, jar, bag, cosmetics package, orclosed-ended tube. The packaging may be fashioned by any means known inthe art, such as by extrusion, coextrusion, thermoforming, injectionmolding, lamination, or blow molding.

Some specific examples of packaging include, but are not limited to,bottles, tips, applicators, and caps for prescription andnon-prescription capsules and pills; solutions, creams, lotions,powders, shampoos, conditioners, deodorants, antiperspirants, andsuspensions for eye, ear, nose, throat, vaginal, urinary tract, rectal,skin, and hair contact; lip product packaging; and caps.

Examples of applicators include lipstick, chapstick, and gloss; packagesand applicators for eye cosmetics, such as mascara, eyeliner, shadow,dusting powder, bath powder, blusher, foundation and creams; and pumpdispensers and components thereof. These applicators are used to applysubstances onto the various surfaces of the body, and reduction ofbacterial growth will be beneficial in such applications.

Other suitable forms of packaging components include drink bottle necks,replaceable caps, non-replaceable caps, and dispensing systems; food andbeverage delivery systems; inhalers in pharmaceutical applications; babybottle nipples and caps; and pacifiers. Where a liquid, solution orsuspension is intended to be applied, the package may be fashioned forapplication in a form for dispensing discrete drops or for spraying ofdroplets.

Examples of end-use applications, other than packaging, in the area offood handling and processing that benefit from antimicrobialfunctionality and wherein microbial growth is reduced in the particularend-use of the consumer are coatings for components of food handling andprocessing equipment, such as temporary or permanent food preparationsurfaces; conveyer belt assemblies and their components; equipment formixing, grinding, crushing, rolling, pelletizing, and extruding andcomponents thereof; heat exchangers and their components; drains andtheir components; equipment for transporting water such as, but notlimited to, buckets, tanks, pipes, and tubing; and machines for foodcutting and slicing and components thereof. Where the surface of suchequipment components is metal, a coating of a polymer could first beapplied to the metal surface. Alternatively, a film of such a polymercould be treated with a solution of chitosan-silver complex and thenheat sealed to the equipment surface. In one embodiment, the equipmentcomponent is a screw for mixing and/or conveying that is an element in asingle-screw or twin-screw extruder, such as, but not limited to, anextruder used for food processing; and the polymer coating comprises anionomer.

Articles treated with a solution of the chitosan-silver complex can alsobe used in or as items of apparel, such as a swimsuit, undergarment,shoe component (for example, a woven or nonwoven shoe liner or insert),protective sports pad, child's garment, or medical garment (such as agown, mask, glove, slipper, bootie, or head covering). Such garmentsparticularly benefit from the inhibition of odor development.

Articles treated with a solution of the chitosan-silver complex can alsobe used in or as medical materials, devices, or implants, such asbandages, adhesives, gauze strips, gauze pads, medical or surgicaldrapes, syringe holders, catheters, sutures, IV tubing, IV bags, stents,guide wires, prostheses, orthopedic pins, dental materials, pacemakers,heart valves, artificial hearts, knee and hip joint implants, bonecements, vascular grafts, urinary catheter ostomy ports, orthopedicfixtures, pacemaker leads, defibrillator leads, ear canal shunts,cosmetic implants, ENT (ear, nose, throat) implants, staples,implantable pumps, hernia patches, plates, screws, blood bags, externalblood pumps, fluid administration systems, heart-lung machines, dialysisequipment, artificial skin, ventricular assist devices, hearing aids,and dental implants.

In the hygiene area, articles that can be treated with a solution of thechitosan-silver complex include personal hygiene garments such asincontinence pads and garments, panty liners, sanitary napkins, sportspads, tampons and their applicators; and health care materials such asantimicrobial wipes, baby wipes, personal cleansing wipes, cosmeticwipes, diapers, medicated wipes or pads (for example, medicated wipes orpads that contain an antibiotic, a medication to treat acne, amedication to treat hemorrhoids, an anti-itch medication, ananti-inflammatory medication, or an antiseptic).

Articles that can be treated with a solution of the chitosan-silvercomplex also include items intended for oral contact, such as a babybottle nipple, pacifier, orthodontic appliance or elastic bands forsame, denture material, cup, drinking glass, toothbrush, or teethingtoy.

Additional child-oriented articles that benefit through treatment with asolution of the chitosan-silver complex include baby bottles, babybooks, plastic scissors, toys, diaper pails, and a container to holdcleansing wipes.

Household articles that can be treated with a solution of thechitosan-silver complex include telephones and cellular phones;fiberfill, bedding, bed linens, window treatments, carpet, flooringcomponents, foam padding such as mat and rug backings, upholsterycomponents (including foam padding), nonwoven dryer sheets, laundrysoftener containing sheets, automotive wipes, household cleaning wipes,counter wipes, shower curtains, shower curtain liners, towels,washcloths, dust cloths, mops, table cloths, walls, and countersurfaces.

Treatment with a solution of the chitosan-silver complex is also usefulin reducing or preventing biofilm growth on the surface of selectiveseparation membranes (for example, pervaporation, dialysis, reverseosmosis, ultrafiltration, and microfiltration membranes), and air andwater filters that comprise at least one polymer, for example,sulfonated aromatic polyamides.

Treatment with a solution of the chitosan-silver complex is also usefulin providing an antifouling surface on boat components such as, but notlimited to, boat hulls, boat parts, and boat motors. If the surface ofthe boat component does not comprise a polymer, for example, if the boatcomponent had a metal surface, a coating of a polymer could first beapplied to the boat component's surface. Alternatively, a polymeric filmcould be treated with the chitosan-silver complex and then heat sealedto the boat component's surface.

Devices used in fluid, e.g., water, transportation and/or storage canalso benefit from the antimicrobial functionality imparted byapplication of the chitosan-silver complex. Exemplary devices include,but are not limited to, pipes and tanks. The inner surface, outersurface, or both surfaces of a pipe or tank can comprise an antifoulingsurface of the invention. If the surface(s) does not comprise a polymer,for example, if the pipe or tank had a metal surface, a coating of apolymer could first be applied to the surface. Alternatively, a film ofsuch polymer could be treated with the chitosan-silver complex and thenheat sealed to the surface(s).

In order to impart antimicrobial functionality to the products listed,the product can be treated with the chitosan-silver complex before it ismanufactured, or after, or at any time during manufacture of theproduct. It is believed that the antimicrobial properties of thematerial will not change significantly.

EXAMPLES

Additional features of the invention are illustrated by the followingExamples.

The meaning of abbreviations is as follows: “h” means hour(s), “min”means minute(s), “sec” means second(s), “d” means day(s), “μL” meansmicroliter, “mL” means milliliters, “L” means liters, “μm” meansmicrometer, “ppm” means parts per million (i.e., milligrams per liter).

Testing Methods for Examples

The antimicrobial effectiveness of the various embodiments of thisinvention was evaluated by using the Antimicrobial Hard Surface TestMethod and the Antimicrobial Hard Surface Wipe Test Method as describedbelow:

Antimicrobial Hard Surface Test Method

The test is conducted using hard polymeric materials that areimpregnated with an antimicrobial agent homogeneously dispersedthroughout the entire thickness of the material (see U.S. Pat. No.3,847,865 for Corian® material plaque preparation). Tiles of the testmaterial are inoculated with a known density of microbial cells andincubated at controlled humidity to retard drying. Following standardmicrobiological techniques for enumerating microorganisms, significantefficacy is demonstrated when at least a 3-log reduction in cell densityon test material compared to control material without antimicrobialagent is achieved.

The relationship between percent reduction and log reduction isconveniently seen by reference to the following:

TABLE 1 Value % Reduction 1 90 2 99 3 99.9 4 99.99 5 99.999

Procedure

-   1. In the chemical fume hood, buff/renew control and test Corian®    6×6 cm tiles by using either a maroon Scotch-Brite™ very fine    abrasive pad (3M #7447) or 200 grit or finer sandpaper. In a    biological safety cabinet, wipe each tile with an isopropanol wipe,    place in a sterile deep petri plate (100×20 mm), air dry, and cover    with the lid.-   2. From an overnight culture grown in Trypticase Soy Broth (TSB) at    25° C., prepare inoculum that is approximately 1×10⁶ cfu (colony    forming units)/ml phosphate buffer*. (Typically an overnight culture    is diluted 1:1,000 in phosphate buffer to yield this density.)    Determine the final cell density by performing a serial-dilution    spread plate count of the inoculum on Trypticase Soy Agar (TSA).-   3. Inoculate each tile by placing 0.5 mL of inoculum on the surface    and spreading evenly with a sterile glass or plastic spreader. The    inoculum should not go over the edge of the tile, but should remain    on the “test side”. Put the lid on the petri plate and place in an    open tray. Incubate in an environmental chamber at 25° C. and 85%    relative humidity (% RH).-   4. To determine speed of kill (i.e., time required to achieve a    3-log or 99.9% reduction) for the antimicrobial tiles, generate a    time-curve by incubating for 1, 2, 3, 4, 6, and 8 h. After the    designated incubation/exposure time, remove the petri plates from    the environmental chamber. In the biological safety cabinet, remove    the petri dish lid and rinse the tile twice with phosphate buffer    using a sterile 5 mL pipet. Use 4.5 mL for the first rinse and 5.0    mL for the second rinse. It is critical to rinse the tile by    repeatedly sucking and expelling the buffer as the pipet is moved    across the entire tile test surface. After the last rinse,    thoroughly wipe the surface with a sterile 1 inch square gauze pad.    Place the gauze into a sterile test tube along with the buffer    rinses.-   5. Determine the bioburden of the rinse buffer using a phosphate    buffer serial-dilution spread plate technique on TSA. Incubate the    plates at the optimal growth temperature and conditions for the test    microorganism for at least 24 h. Count the colonies on plates and    calculate the density taking into account all dilutions. Report the    findings as cfu/ml.-   6. The Δt value may be calculated as follows: Δt=C−B, where Δt is    the activity constant for contact time t, C is the mean log₁₀    density of microbes rinsed off of control tiles after X hours of    incubation, and B is the mean log₁₀ density of microbes rinsed off    of test tiles after X hours of incubation.

*Stock Phosphate Buffer: Monobasic Potassium Phosphate 22.4 g DibasicPotassium Phosphate 56.0 g Deionized Water to 1000 mL

-   -   Adjust to pH 6.0-7.0 with either NaOH of HCl, filter, sterilize,        and store at 4° C. until use.

Working Phosphate Buffer:

-   -   Dilute 1 mL of stock phosphate buffer in 800 mL of sterile        deionized water (pH should be 6.0-7.0), dispense in working        volumes and autoclave.

Antimicrobial Hard Surface Wipe Test Method

Summary of Method

This test is used to determine the frequency of renewal required for anantimicrobial surface that can be regenerated by buffing with anabrasive pad or sandpaper. The experimental design described below canbe used to determine the duration of antimicrobial efficacy under normaluse conditions. A surface with “reduced activity” is one in which theantimicrobial activity has fallen below a 3-log reduction capability.

Wiping with Damp Cloth: Soapy Water

The purpose of this protocol is to determine the effect of repeatedtypical clean-ups with soapy water on the durability of the efficacy ofantimicrobial surfaces.

-   1. Prepare a set of control and test tiles as described in the    “Antimicrobial Hard Surface Test Method”.-   2. Wipe each tile set with a sterile cloth (e.g. cheesecloth,    typical cotton kitchen towel, sponge, pre-moistened wipe, etc.)    dampened with soapy water. The preparation of the soapy water is per    the soap manufacturer's label instructions. Completely soak the    cloth in the soapy water and hand wring prior to each use. A back    and forth motion is used to completely wipe the surface of each    tile.-   3. After each wipe, rinse the tile with sterile deionized water to    remove any soap residue and air dry.-   4. After each set of 50 wipes, test the control and test tiles for    antimicrobial efficacy using the “Antimicrobial Hard Surface Test    Method”.-   5. Continue test in sets of 50 wipes until either an expected use    period is satisfied or until the antimicrobial surface shows reduced    activity. When Δt<3.0, the test tile is considered to have reduced    activity.    Wiping with Damp Cloth: Liquid or Spray Disinfectant/Sanitizer

The purpose of this protocol is to determine the effect of repeatedtypical clean-ups with liquid disinfectants or sanitizers on thedurability of the efficacy of antimicrobial surfaces.

-   1. Prepare a set of control and test tiles as described in the    “Antimicrobial Hard Surface Test Method”.-   2. Manufacturers use directions for each disinfectant/sanitizer are    not consistent. In order to standardize the exposure conditions, use    the following directions. For liquid products, completely soak a    sterile cloth in the disinfectant/sanitizer solution prepared    according to the manufacturer's label directions and hand wring    prior to each use. Wipe each tile with a back and forth motion to    completely cover the surface of each tile. For spray products, spray    the tile surface twice to ensure a thorough wetting and wipe once    using a back and forth motion with a sterile cloth.-   3. After each set of 50 wipes, test the control and test tiles for    antimicrobial efficacy using the “Antimicrobial Hard Surface Test    Method”.-   4. Continue test in sets of 50 wipes until either an expected use    period is satisfied or until the antimicrobial surface shows reduced    activity. When Δt<3.0, the test tile is considered to have reduced    activity.

Shake Flask Test for Antimicrobial Testing of Materials

The following procedure was used to test the nonwoven samples in Example9 for antimicrobial activity:

1. Inoculate a single, isolated colony from a bacterial or yeast agarplate culture in 15-25 ml of Trypticase Soy Broth (TSB) in a sterileflask. Incubate at 25-37° C. (use optimal growth temperature forspecific microbe) for 16-24 h with or without shaking (selectappropriate aeration of specific strain). For filamentous fungi, preparesporulating cultures on agar plates.

2. Dilute the overnight bacterial or yeast culture into sterilephosphate buffer (see below) at pH 6.0 to 7.0 to obtain approximately10⁵ colony forming units per ml (cfu/ml). The total volume of phosphatebuffer needed will be 50 ml×number of test flasks (including controls).For filamentous fungi, prepare spore suspensions at 10⁵ spores/ml. Sporesuspensions are prepared by gently resuspending spores from an agarplate culture that has been flooded with sterile saline or phosphatebuffer. To obtain initial inoculum counts, plate final dilutions(prepared in phosphate buffer) of 10⁻⁴ and 10⁻³ onto Trypticase Soy Agar(TSA) plates in duplicate. Incubate plates at 25-37° C. overnight.

3. Transfer 50 ml of inoculated phosphate buffer into each sterile testflask containing 0.5 g of material to be tested. Also, prepare controlflasks of inoculated phosphate buffer and uninoculated phosphate bufferwith no test materials.

4. Place all flasks on a wrist-action shaker and incubate with vigorousshaking at room temperature. Sample all flasks periodically and plateappropriate dilutions onto TSA plates. Incubate at 25 to 37° C. for 16to 48 h and count colonies.

5. Report colony counts as the number of Colony Forming Units per ml(cfu/ml).

6. The Δt value may be calculated as follows: Δt=C−B, where Δt is theactivity constant for contact time t, C is the mean log₁₀ density ofmicrobes in flasks of untreated control materials after X hours ofincubation, and B is the mean log₁₀ density of microbes in flasks oftreated materials after X hours of incubation. Δt is typicallycalculated at 4, 6, or 24 hours and may be expressed as Δt_(x).

Stock phosphate buffer: Monobasic Potassium Phosphate: 22.4 g DibasicPotassium Phosphate: 56.0 g Deionized Water: Bring up volume to 1000 ml

Adjust the pH of the phosphate buffer to pH 6.0 to 7.0 with either NaOHor HCl, filter, sterilize, and store at 4° C. until use. The workingphosphate buffer is prepared by diluting 1 ml of stock phosphate bufferin 800 ml of sterile deionized water.

Example 1 Preparation of Chitosan-Silver Nitrate Complexes

Chitosan (42 g, ChitoClear® food grade chitosan, Primex, Iceland) wasdissolved in 2% aqueous acetic solution (1100 mL) and stirredvigorously. A solution of silver nitrate (30 g) in deionized water (100mL) was added over a period of 10 min. A clear, thick gel resulted.Additional water (300 mL) was added to the gel and stirred for 30 min.Concentrated ammonium hydroxide was added in drops to raise pH to 7-8.The product was filtered, washed with water (4×500 mL), and then withacetonitrile (4×500 mL). The resulting product was dried under vacuumfor two days, ground to a fine powder, and used as such in the Corian®AB™ material preparation. Yield of the product was 53.7 g. The amount ofsilver in the complex was determined by Inductively Coupled Plasmaspectroscopy (ICP), which is an atomic emission spectroscopy method inwhich inductively coupled plasmas are used as the excitation source(see, for example, Inductively Coupled Plasma Emission Spectroscopy, pt.1, P. W. J. M. Boumans, John Wiley & Sons (New York, N.Y.), 1987, pp.2-3). ICP silver metal analysis of this material indicated theproportion of silver to be 13.5% by weight.

In contrast, when a chitosan/silver complex was prepared by treating asuspension of chitosan with silver nitrate solution, the resultantproduct visually appeared the same as the starting material, did notform a gel, and had not dissolved in deionized water even after twodays. The absence of swelling of this preparation clearly indicates thelack of cross linking of chitosan chain by silver and it is likely thatthe metal is distributed more on the surface of the chitosan thandispersed within it.

Example 2 Preparation of Chitosan-Silver Nitrate Complexes with VaryingSilver Content

Five solutions of chitosan (20 g each, ChitoClear®, Primex, Iceland) in500 mL of water containing 7.5 mL of acetic acid were treatedsuccessively with aqueous solutions (50 mL) of silver nitrate in thefollowing proportions. Solution A in 7.2 g, B=3.6 g, C=1.8 g, D=0.9 g,E=0.45 g of silver nitrate. The reaction was conducted and processed asdescribed in the previous Example. Yield of the products 1A through 1Eranged from 25 to 30.0 g.

Silver Content by ICP Analysis:

-   -   1A=10.5% silver    -   1B=9.5% silver    -   1C=5.1% silver    -   1D=2.2% silver    -   1E=1.6% silver

In the following Examples 3-5, Corian® material plaques, 6 cm by 6 cm byabout 1.3 cm, containing additives as indicated, were prepared accordingto U.S. Pat. No. 3,847,865.

Example 3

In the first plaque preparation, plain chitosan powder (ChitoClear®,Primex, Iceland) in 0.5%, 1.0%, and 3% concentrations by weight wereadded to the Corian® material mix and cast into plaques. As shown inFIG. 1, no significant antimicrobial activity was observed for thesesamples.

Example 4

Chitosan-silver nitrate powder from Example 1 was added to the plaquemixtures in 0.1%, 0.25%, 0.5%, and 1.0% concentrations by weight. Theeffective concentrations of the silver in these samples based on theadditives were 0.01%, 0.03%, and 0.13%, respectively. These plaquesexhibited effective antimicrobial activity as shown in FIG. 2.

Example 5

The following five Corian® material plaques were made as described inExample 4, except the chitosan concentration in all of thesepreparations was maintained at 1% by weight and the amount of silvernitrate relative to chitosan was changed using the material described inExample 2. Thus, the amounts of chitosan-silver in samples A to Erespectively, were: 1:0.105; 1:0.095; 1:0.05; 1:0.022; 1:0.016. Allthese plaques exhibited bactericidal activity against a variety oforganisms as shown in FIGS. 3 through 9.

In addition, these chitosan-silver Corian® material plaques maintainedantimicrobial activity against Escherichia coli O157:H7 (FIG. 10), amicrobe that is difficult to kill, and against Escherichia coli ATCC25922 (FIG. 11) in the presence of “soil”. Bovine serum albumin (BSA)was added at 1.15 g per liter of phosphate buffer and utilized toprepare the inoculum as described for the “Antimicrobial Hard SurfaceTest Method”. This is a significant finding since many antimicrobialsurfaces are inactivated in the presence of “soil”, as can be seen withthe Corian®AB™ material positive control that was rendered ineffectiveagainst E. coli O157:H7 (FIG. 10).

Example 6 Preparation of Chitosan-Zinc Sulfate for Use as Additives inCorian® Material Plaques

Chitosan (40.5 g, ChitoClear®, Primex, Iceland) was dissolved in 2%aqueous acetic acid (1000 mL) and was vigorously stirred. To this, asolution of zinc sulfate (44.0 g) in water (100 mL) was added in drops.A viscous solution was obtained. To this, 250 mL of acetone was added toprecipitate the product, which was filtered, washed with deionizedwater, and acetonitrile. It was dried under vacuum and ground to a finepowder (about 400 mesh size; 64 g). This preparation providedantimicrobial plaques against Gram positive and Gram negative bacteriaas well as against yeasts as indicated in FIGS. 12, 13, and 14.

Example 7 Preparation of Chitosan-Copper Sulfate Complexes forIncorporation into Corian® Material Plaques

Chitosan (20.0 g, ChitoClear®, Primex, Iceland) was dissolved in 1.5%aqueous acetic acid (650 mL) and was vigorously stirred. To this, asolution of copper sulfate (25.0 g) in water (140 mL) was added indrops. A fibrous precipitate was obtained, which was filtered, washedwith deionized water, and acetonitrile. It was dried under vacuum andground to a fine powder (42 g).

Corian® material plaques containing 0.5%, 1.0%, 2.0%, and 3.0%concentration by weight of the chitosan-copper sulfate powder wereprepared and evaluated for their antimicrobial properties (FIG. 15).

Example 8 Preparation of Chitosan-Silver Nitrate Complexes

Chitosan (150 g, ChitoClear®) food grade, Primex, Iceland) was dissolvedin 1.3% aqueous acetic solution (3800 mL) and stirred vigorously. Asolution of silver nitrate (14.5 g) in deionized water (75 mL) was addedover a period of 10 min. A clear, thick gel resulted. Additional water(400 mL) was added to the gel and stirred for 30 min. Concentratedammonium hydroxide was added in drops to raise pH to 7-8. The productwas filtered, washed with water (2×1000 mL), and then stirred inacetonitrile (1000 mL), filtered, and washed again with acetonitrile(1000 ml). The resulting product was dried under vacuum for two days toget a fibrous product (195 g). This was ground to a fine powder underliquid nitrogen temperture. The amount of silver in the complex wasdetermined by Inductively Coupled Plasma spectroscopy (ICP), which is anatomic emission spectroscopy method in which inductively coupled plasmasare used as the excitation source (see, for example, Inductively CoupledPlasma Emission Spectroscopy, pt. 1, P. W. J. M. Boumans, John Wiley &Sons (New York, N.Y.), 1987, pp. 2-3). ICP silver metal analysis of thismaterial indicated the proportion of silver to be 4% by weight.

Example 9 Nonwoven Fabric Treated with Chitosan-Silver Complex Solution

0.9% Chitosan solution (ChitoClear® food grade, Primex, Iceland) in 0.5%aqueous acetic solution was made. Chitosan-silver powder (9.0 g) fromExample 8 was added and dissolved to give a chitosan solution containingabout 3600 ppm of silver. A nonwoven fabric (55% pine wood pulp/45% PET,2 oz/yd²) was passed through deionized water and then through thechitosan-silver solution, squeezed between rollers and dried in hot air(115° C.) and wound. This was tested for antimicrobial activity againstE. Coli ATCC # 25922.

TABLE 2 E. coli ATTC E. coli ATCC E. coli ATCC 25922 25922 25922 LogReduction Log Reduction Log Reduction after after after Sample 1 hour 4hours 8 hours Uninoculated buffer 0 0 0 Inoculated Buffer −0.62 −0.54−0.57 Fabric with 5.1 5.1 5.1 chitosan-silver complex

1. A method for producing a chitosan-silver complex, the methodcomprising the sequential steps of: (a) dissolving 0.25 to 8.0% byweight chitosan in an acid solution; (b) adding a solution of a silversalt to the product of step (a); (c) adding water to the product of step(b), with stirring; (d) raising the pH of the product of step (c) to pH7 to 8 by adding a basic solution; (e) filtering the product of step(d); (f) washing the filtered solids obtained in step (e) with water,(g) washing the solids of step (f) with acetonitrile; (h) drying thewashed solids under vacuum to obtain the chitosan-silver complex; and(i) optionally, grinding the dried product of step (h) to a fine powder.2. The method of claim 1, wherein the acid solution is a 0.25 to 5%aqueous solution of acetic acid; the silver salt solution is 0.5 to 20wt % silver nitrate in water; and the pH is raised in step (d) byaddition of aqueous ammonium hydroxide or substituted ammoniumhydroxide.
 3. A chitosan-silver complex produced by the method ofclaim
 1. 4. A finish solution for textile applications comprising thechitosan-silver complex of claim 3.